1. Field of the Invention
The present invention relates to a method for producing a Group III nitride semiconductor light-emitting device, whose characteristic feature resides in a process for forming a n-type layer, and more particularly a process that can prevent the deterioration of characteristics of the p cladding layer. Moreover, the Group III nitride semiconductor light-emitting device whose characteristic feature resides in a structure of the p-type layer.
2. Background Art
A Group III nitride semiconductor light-emitting device has a structure mainly comprising a substrate on which am n-type layer, a light-emitting layer, and a p-type layer are sequentially deposited. The p-type layer has a structure in which a p cladding layer, and a p contact layer are sequentially deposited in this order on the light-emitting layer.
The p cladding layer, for example, is an AlGaN single layer or has a superlattice structure in which AlGaN and InGaN or AlGaN and GaN are alternately deposited more than once. The p cladding layer is grown at a low temperature of 800° C. to 950° C. to reduce thermal damage to the light-emitting layer.
The p contact layer is formed of, for example, p-GaN doped with Mg at a high concentration. The p contact layer is grown at temperature of 950° C. to 1100° C., which is higher than the growth temperature of the p cladding layer to improve crystal quality.
In order to grow the p cladding layer at a low temperature, and the p contact layer at a high temperature, conventionally, after the p cladding layer was grown, crystal growth is stopped and the temperature is increased. Then, the p contact layer is grown.
As a technique related to the present invention, there is Japanese Patent Application Laid-Open (kokai) No. 2000-164512 or 2007-80996. Japanese Patent Application Laid-Open (kokai) No. 2000-164512 discloses a Group III nitride semiconductor light-emitting device wherein a p-AlGaN capping layer, a p-GaN optical waveguide layer, a p-AlGaN p cladding layer, and a p-GaN p contact layer are sequentially deposited on a light-emitting layer.
Japanese Patent Application Laid-Open (kokai) No. 2007-80996 discloses a Group III nitride semiconductor light-emitting device wherein a GaN layer having a thickness or 100 nm and a Mg concentration of 5×1019/cm3 is formed between a p cladding layer having a superlattice structure in which AlGaN and GaN are alternately deposited more than once, and a p contact layer formed of InGaN doped with Mg.
However, during heating for formation of the p contact layer after the p cladding layer was formed, Mg is excessively doped into the p cladding layer or other impurities are mixed into the crystal due to the exposed surface of the p cladding layer. This causes adverse effect on characteristics, such as increased resistivity of the p cladding layer.
Moreover, in Japanese Patent Application Laid-Open (kokai) No. 2000-164512 or 2007-80996, there is no description about a deterioration of characteristics of the p cladding layer. Japanese Patent Application Laid-Open (kokai) No. 2007-80996 does not reveal for what purpose the GaN layer is formed between the p cladding layer and the p contact layer.